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AndreaNobili
Asked: 2020-03-20 15:18:09 +0800 CST

After a restart due to a system crash the ethernet interface is disappeared. How to restore it?

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I am not so into Linux and I am experiencing a very strange problem with a Linux 19.10 system on which I am working into VmWare workstation (but I suppose that it is not a VMware related problem).

The problem is that I had to restart the system due to a crash that freeze the system. After the restart I have no more Internet connection.

Performing the ifconfig command into the shell I obtain:

developer@developer-virtual-machine:/etc/network$ ifconfig
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Loopback locale)
        RX packets 2508  bytes 186240 (186.2 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 2508  bytes 186240 (186.2 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

So it seems that for some reason it loose the ethernet interface used by VmWare to connect in NAT mode.

I tried to restart the system (also the host Windows machine on which VMWare is installed) but I still have this problem. How can I try to fix it?

EDIT-1: Performing sudo lshw -C network I obtain this output:

developer@developer-virtual-machine:~$ sudo lshw -C network
[sudo] password di developer: 
  *-network DISABLED        
       description: Ethernet interface
       product: 82545EM Gigabit Ethernet Controller (Copper)
       vendor: Intel Corporation
       physical id: 1
       bus info: pci@0000:02:01.0
       logical name: ens33
       version: 01
       serial: 00:50:56:3a:4b:1e
       size: 1Gbit/s
       capacity: 1Gbit/s
       width: 64 bits
       clock: 66MHz
       capabilities: pm pcix bus_master cap_list rom ethernet physical logical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=e1000 driverversion=7.3.21-k8-NAPI duplex=full latency=0 link=no mingnt=255 multicast=yes port=twisted pair speed=1Gbit/s
       resources: irq:19 memory:fd5c0000-fd5dffff memory:fdff0000-fdffffff ioport:2000(size=64) memory:fd500000-fd50ffff

It seems that the networking is disabled

networking network-manager ifconfig ethernet 19.10

2 Answers

  1. Best Answer

    Solved myself. Maybe it can help someone else:

    1) I discovered that Ubuntu 19.10 by default is not defining the network interfaces by the /etc/network/interfaces file. This file doesn't exist. To manage the network interfaces it is using the network manager: http://manpages.ubuntu.com/manpages/cosmic/man1/nmcli.1.html

    2) First of all I list the interfaces by this command: sudo nmcli device show

    [sudo] password di developer: 
GENERAL.DEVICE:                         ens33
GENERAL.TYPE:                           ethernet
GENERAL.HWADDR:                         00:50:56:3A:4B:1E
GENERAL.MTU:                            1500
GENERAL.STATE:                          10 (non gestito)
GENERAL.CONNECTION:                     --
GENERAL.CON-PATH:                       --
WIRED-PROPERTIES.CARRIER:               off
IP4.GATEWAY:                            --
IP6.GATEWAY:                            --

GENERAL.DEVICE:                         lo
GENERAL.TYPE:                           loopback
GENERAL.HWADDR:                         00:00:00:00:00:00
GENERAL.MTU:                            65536
GENERAL.STATE:                          10 (non gestito)
GENERAL.CONNECTION:                     --
GENERAL.CON-PATH:                       --
IP4.ADDRESS[1]:                         127.0.0.1/8
IP4.GATEWAY:                            --
IP6.ADDRESS[1]:                         ::1/128
IP6.GATEWAY:                            --
IP6.ROUTE[1]:                           dst = ::1/128, nh = ::, mt = 256

    As you can see the ethernet network interface neamed ens33 is at the moment not handled (in italian "non gestito"), so at the moment is disabled.

    3) I enabled it by 

    nmcli networking on

    now it works fine

    • 5

  2. Here is what fixed the same problem for me (AndreaNoboli's answer sadly didn't help):

    check /etc/NetworkManager/NetworkManager.conf and /etc/NetworkManager/conf.d/ to see if there's a managed=false entry which could be changed.

    I got it from an only tangentially related issue elsewhere: https://access.redhat.com/discussions/6278791, but it worked perfectly for me.

    • 1